X-Ray Diffraction

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What is X-Ray Diffraction?

X-ray diffraction is a non-destructive solid technique for delineating crystalline materials. It gives information on phases, structures, favoured crystal orientations (texture), and different structural parameters, such as strain, crystallinity, medium grain size, and crystal cracks. XRD peaks are designed by the constructive intervention of a monochromatic beam of X-rays interspersed at distinct angles from each collection of lattice planes in a specimen. The peak intensities are defined by the atomic positions inside the lattice planes. 


Consequently, the XRD design is the fingerprint of periodic atomic methods in a dispensed material. A standard database of online research for X-ray powder diffraction patterns allows quick phase identification for a wide variety of crystalline samples. X-ray diffraction results from radiation being scattered by a regular array of scattering centers whose spacing is the same as the radiation. Diffraction gratings need to have spacings equivalent to the wavelength of diffracted radiation.


X-Ray Diffraction Analysis

X-ray diffraction analysis (XRD) is a method used in materials science to determine the material’s crystallographic structure. XRD operates by measuring the X-rays’ intensities and scattering angles that leave the material.


The primary use of X-ray diffraction analysis is the identification of materials based on their diffraction pattern. The x-ray diffraction method in phase identification also gives information on how the ideal structure differs from the exact one, owing to internal defects and stresses.

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How Does it Work?

Crystals are periodic arrays of atoms, whilst X-rays can be deemed as waves of electromagnetic radiation. Crystal atoms scatter incident X-rays, mainly through interaction with the atoms’ electrons. This occurrence is identified as elastic scattering; the electron is known as the scatterer. A regular array of scatterers presents a constant array of orbicular waves. In the bulk of directions, these waves eliminate each other out through destructive interference; however, they combine constructively in less explicit directions, as defined by Bragg’s law:

2d sinθ = nλ

here, 

d is the space between the diffracting planes,

θ (theta) = incident angle, 

n = integer 

and 

λ = beam wavelength 

The particular directions resemble spots on the diffraction pattern called reflections. Consequently, impinging on a regular array of scatterers, the X-ray diffraction patterns emerge from the electromagnetic waves. To form the X-ray diffraction pattern x-rays are used, because their wavelength, λ, is mostly in the same order of magnitude as the spacing, d, between the crystal planes (1-100 angstroms).


X-Ray Diffraction By Crystals

X-ray diffraction by crystals can be exactly as the visible light is diffracted by a diffraction grating; in other words, we can state that crystals can be used as diffraction gratings for diffraction X-rays. Von Laue first conceived this important concept in 1912, and consequently, it was tested by Freidrich and Knipping. They confirmed that an X-ray beam passing through a single crystal was undoubtedly split up into a set of diffracted beams.


The x-ray diffraction by crystals is the only connection with the direct exploration of the crystals’ interior; that is, in connection with the fixations of the atoms’ position on the crystal lattice, the measurement of the distances between atoms and the associated internal symmetry.


Such a study is suitable because the intensities of diffracted beams and their directions are related to crystals’ atomic arrangements. Thus, measurements of their directions and intensities would present the desired information about crystals. 


X-Ray Diffraction Pattern

An X-ray diffraction pattern is the intensity plot formed when the sample scatters x-rays in question at varying degrees. There is a unique X-Ray pattern for each “phase.” In a mixture, the x-ray diffraction pattern is the addition of patterns of the individual phases. On the other hand, any observed XRD pattern is, in reality, an addition/sum of patterns generated by separate stages within a mix. Data from x-ray diffraction experiments are compared with reference pattern data to understand the phases present in a sample.

FAQs (Frequently Asked Questions)

Q1. Describe the Important X-Ray Diffraction Technique.

Answer: The important X-Ray diffraction technique is:

  • Single-crystal Crystallography: A high-quality single crystal is raised and set in different introductions in the x-ray beam. Single-crystal measurements usually yield more data than other X-Ray diffraction techniques, but they are also the most challenging. Protein crystallography is an important application of single-crystal diffraction. It is a central technique in modern molecular biology.

  • Powder Diffraction: This a technique that uses finely ground powder instead of a mixture of crystallites. Here, the diffraction pattern is formed through concentric rings. This technique is utilized in two complementary ways. One is in the form of a substitute to the single-crystal technique, and the other is for the purpose of identifying phases in mineralogy. 

Q2. What are the Steps Involved in an X-Ray Diffraction Instrument?

Answer: The x-ray diffraction instrumentation is a culmination of different components in a synchronized manner in order to initiate the diffraction. The various steps involved are:

  • X-rays: The basic component is the x-ray generation instrument. X-rays are generated by different methods such as “X-ray tubes, rotating anode x-ray generator, microfocus tube, and synchrotron.”

  • Collimation: The x-rays generated by any of the different methods are consisting of a range of wavelengths.  These varied wavelengths are narrowed down to a thin beam comprising a smaller wavelength spread in a particular direction with collimation. This can be executed with the help of “pinholes or slits, x-ray mirror, crystal monochromator, and multilayer optics.”

  • Detection: Lastly, the process culminates with the detection of the scattered x-rays. The detection process has evolved over the years, starting with the very basic films, followed by the scintillation detectors and the 2D detector.

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